Characteristics of French methicillin-resistant Staphylococcus aureus isolates with decreased susceptibility or resistance to glycopeptides

Abstract

According to the French Society of Microbiology, Staphylococcus aureus isolates are suspected to have decreased susceptibility to glycopeptide(s) when at least one colony is able to grow from an inoculum of 10 microL of 2 McFarland bacterial suspension plated on Mueller-Hinton agar containing 5 mg/L teicoplanin and incubated for 48 h at 35-37 degrees C. We analysed 89 methicillin-resistant S. aureus isolates (MRSA), collected in 2000-2001 from 24 hospitals located in 18 French cities, which were able to grow on this selective medium. These isolates were distributed into six groups on the basis of their glycopeptide resistance phenotypes: (A) glycopeptide susceptible (GSSA, 21 isolates); (B) heterogeneous teicoplanin intermediately resistant (hetero-TISA, 24 isolates); (C) heterogeneous and intermediately resistant to both glycopeptides, teicoplanin and vancomycin (hetero-GISA, six isolates); (D) heterogeneous vancomycin intermediately resistant/teicoplanin intermediately resistant (hetero-VISA/TISA, 30 isolates); (E) GISA (four isolates); (F) TISA (four isolates). Despite the persistent decrease in gentamicin-resistant MRSA isolates in French hospitals since 1993, their prevalence is very high in groups D, E and F. Moreover, most of the group C, D and E isolates exhibiting decreased susceptibility to both glycopeptides belong to the same major SmaI genotype, which has been detected in Europe since at least 1989.

Increased Vancomycin MICs for Staphylococcus aureus Clinical Isolates from a University Hospital during a 5-Year Period

“…aureus clinical isolates with reduced susceptibility to vancomycin have been reported from selected patient populations and study sites using various testing methods (e.g., agar dilution, broth microdilution, Etest, agar screening, and population studies) (2,9,15,16,32). However, only a few cases of VRSA or VISA infections have been documented to date.…”

“…Since then, six confirmed vancomycin-resistant S. aureus (VRSA) (MIC Ն 32 g/ml) (3-5, 30, 32; L. M. Weigel, personal communication) and at least 21 vancomycin-intermediate S. aureus (VISA) (17,33) strains have been documented in the United States. A considerable prevalence of heterogeneous VISA (hVISA), in which only a subset of the bacterial population expresses the resistant phenotype, has been reported among S. aureus isolates from various geographic and patient populations of the world (9,12,27,32,33).…”

Glycopeptide resistance in Staphylococcus aureus: is it a real threat?

“…32 In France, 640 isolates were screened and only 3 distinct isolates with reduced susceptibility to vancomycin and teicoplanin were obtained. 33 What is the mechanism of glycopeptide resistance in S. aureus?…”

Glycopeptide resistant Staphylococcus

“…There are, however, a few clinical isolates which are resistant to teicoplanin and fully susceptible to vancomycin (Kaatz et al., 1990; El Solh et al., 2003; Monecke et al., 2003). In the first described clinical case vancomycin treatment was still successful (Kaatz et al., 1990).…”